Cod Tagging in the Newfoundland Area During 1947 and 1948

Abstract

About 4200 cod were tagged in the Newfoundland and Labrador inshore areas and on the Grand Bank and St. Pierre Bank. The migrations of tagged cod are described from tagging in the inshore fishing areas off Nutak and Domino in Labrador, off Englee, St. John's, Burin and Corbin, and Lark Harbour in Newfoundland and on the Grand Bank and St. Pierre Bank. Most cod tagged in the inshore areas were recaptured close to the tagging areas with a gradual increase with time after tagging in the average minimal distance moved. There is, at least in many areas, a southward winter and a northward spring and early summer movement of cod.The greatest number of recaptures (after the tagging year) of cod tagged inshore were in the shallow waters of the inshore area from June–September. From July to February–March recaptures were from progressively deeper water with some recaptures in the shallow inshore waters by May and many by June. Some recaptures, however, were still from deep water in June–September.Cod caught inshore by commercial fishermen and offshore by research otter trawler were tagged, some with an external, combination cellulose nitrate and aluminum disc bachelor-button tag inserted through the opercular bone, some with a 2-inch, flat cellulose nitrate tag inserted in the body cavity through a posterior slit in the body wall. Injuries at the point of insertion of the tag were often quite severe for the external, but generally mild for the internal tags, long after the time of tagging. The internal tags gave fewer returns than the external tags in the tagging year, but the opposite was generally true for the years following. In years after the tagging year the percentage recaptures of smaller cod were greatly in excess of those of larger cod. In the year after the tagging year smaller tagged cod — those up to 60 or 70 cm — showed less significant movement than larger tagged cod. Although cod were recaptured almost immediately after being tagged from traps, those tagged from handlines and linetrawls were not caught by baited hooks for 7–10 days afterwards. An inverse relationship exists between the length of otter-trawl drag from which fish were tagged and the percentage recaptures.